I spent almost a year with a singer/keyboardist trying to get a cover band going. All we needed was a good drummer and guitarist. Couldn't get anyone. The people who did want to join were not up to snuff; the people who were up to snuff would say, "Well, call me back when you have a drummer" (if a guitarist) or vice versa (if a drummer). Nine or ten months of this and we could never get four people in the same room at the same time, and finally abandoned the project.
The point being, creating a startup from scratch is hard, indeed next to impossible. It's not that something is wrong with your ad, it's your situation. If you're relying on craigslist to recruit the whole band, that immediately says that you don't know anyone. If you don't know anyone, you probably don't have any experience, no contacts, probably don't have a PA... may or may not be true, but that's what I would assume. So people are going to pass. If a person DOES show up, it's you and him, alone in your basement with a lot of talk about this great band you want to start but no reality to it - and the other guy will say, "call me again when you have some more people." By the time you have the other people he will have moved on to another project.
So what do you do? Network. Go audition for other people's bands that seem like they might be interesting. You may find a great project you want to be a part of, or at the least you get to meet folks. Maybe there's someone out there trying to launch a band with drums and guitar but they don't have a bassist. Go to open mics and jam with people. If you're a regular, they'll get to know you.
I'd also suggest, instead of a whole big ad calling for the creation of an entire band from scratch, put something more low-key out there, just that you want to jam with folks and the kinds of things you like. If you get together with a guitarist to jam a few times, that's cool. Then after a few weeks maybe you find a drummer who wants to jam too. If everyone clicks over a couple of months, you say, "Hey, let's work up some originals and try playing them out." But if you "audition" a guitarist for a band that doesn't exist, you'll get "call me later."